Nonaqueous electrolyte solution and lithium secondary battery using same

ABSTRACT

A nonaqueous electrolytic solution that provides a lithium secondary battery with excellent electrical capacity, cycling properties, storage properties and other battery characteristics and that maintains the battery characteristics for a long time; and a lithium secondary battery comprising it. A nonaqueous electrolytic solution comprising an electrolytic salt dissolved in a nonaqueous solvent, containing 0.1 to 10% by weight of an ethylene carbonate derivative represented by the general formula (I), and 0.01 to 10% by weight of (A) a triple bond-containing compound and/or (B) a pentafluorophenyloxy compound represented by the general formula (X), wherein formula (I) is: 
     
       
         
         
             
             
         
       
     
     wherein R 1  to R 3  each independently represents a hydrogen atom, a halogen atom, an alkenyl group, an alkynyl group or an aryl group, provided that ethylene carbonate is excluded from the definition of the ethylene carbonate derivative; and wherein formula (X) is: 
     
       
         
         
             
             
         
       
     
     wherein R 15  represents an alkylcarbonyl group, an alkoxycarbonyl group, an aryloxycarbonyl group or an alkanesulfonyl group.

TECHNICAL FIELD

The present invention relates to a nonaqueous electrolytic solutioncapable of forming a lithium secondary battery exhibiting excellentbattery characteristics such as electrical capacity, cycle property andstorage property, and to a lithium secondary battery using thenonaqueous electrolytic solution.

BACKGROUND ART

In recent years, lithium secondary batteries have been widely used asdriving power supplies for small electronic devices and the like. Suchlithium secondary batteries are mainly constituted of a positiveelectrode comprised of a lithium compound oxide, a negative electrodecomprised of a carbon material or a lithium metal, and a nonaqueouselectrolytic solution. As the nonaqueous electrolytic solution, acarbonate such as ethylene carbonate (EC) and propylene carbonate (PC)is used.

A lithium secondary battery using, for example, LiCoO₂, LiMn₂O₄ orLiNiO₂ as a positive electrode material brings about a reduction of thebattery performance, when part of the solvent of the nonaqueouselectrolytic solution locally undergoes an oxidative decompositionduring the charging, because the decomposition products inhibit thedesired electrochemical reaction of the battery. Such a reduction isconsidered to be attributed to an electrochemical oxidation of thesolvent at the interface between the positive electrode material and thenonaqueous electrolytic solution.

Also, a lithium secondary battery using, for example, a highlycrystallized carbon material, such as natural graphite and artificialgraphite, as a negative electrode material brings about a reduction ofthe battery performance, when the solvent of the nonaqueous electrolyticsolution undergoes a reductive decomposition on the surface of thenegative electrode during the charging. Even in the case of EC which iswidely generally used as a solvent for the nonaqueous electrolyticsolution, a part thereof undergoes a reductive decomposition duringrepeated charging and discharging.

As techniques for improving the battery characteristics of such lithiumsecondary batteries, there are known, for example, Patent Documents 1 to9.

Patent Document 1 discloses a nonaqueous electrolytic solution for asecondary battery composed of an electrolyte and a non aqueous solventcontaining a cyclic carbonate having a nonconjugated unsaturated bond,such as vinylethylene carbonate (VEC), in an amount of 0.1 to 20% byweight based on the entire nonaqueous solvent and suggests animprovement of cycle life as its feature. The battery containing VEC,however, has a problem that a gas due to decomposition of theelectrolytic solution is generated at the negative electrode in a largeramount as compared with a battery without VEC, thereby to cause areduction of the battery performance.

Patent Document 2 discloses a lithium secondary battery using a mixtureof an ethylene carbonate derivative, such as VEC and monofluoroethylenecarbonate, and triphenyl phosphate. With such an electrolytic solutionsystem, however, satisfactory cycle characteristics are not obtainable.Further, sufficient initial capacity and cycle characteristics cannot beobtained when the charge final voltage of the battery is higher (4.3 Vor higher) than the conventional one.

Patent Documents 3 to 6 disclose a nonaqueous electrolytic solution fora lithium secondary battery containing an alkyne derivative.

Patent Document 7 discloses a coin-shaped battery as a lithium secondarybattery containing a pentafluorobenzene compound, such aspentafluoroanisole, having an electron donating group. The coin-shapedbattery, however, shows retention of capacity after 200 cycles of onlyabout 80% and, therefore, has insufficient cycle property.

Patent Document 8 discloses that pentafluoroanisole is usable as anoxidation reduction reagent as chemical means for protecting anonaqueous electrolytic solution secondary battery from overcharge butdoes not mention the cycle property thereof. Patent Document 9 disclosesa nonaqueous electrolytic solution for a lithium secondary batterycontaining a pentafluorophenyloxy compound.

In these nonaqueous electrolytic solutions, the cycle property, etc. areimproved in a certain degree. However, further improvement of batteryperformance is needed.

-   [Patent Document 1] Japanese Patent Application Publication    2000-40526-   [Patent Document 2] U.S. Patent Application Publication 2003/157413-   [Patent Document 3] Japanese Patent Application Publication    2000-195545-   [Patent Document 4] Japanese Patent Application Publication    2001-313072-   [Patent Document 5] Japanese Patent Application Publication    2002-100399-   [Patent Document 6] Japanese Patent Application Publication    2002-124297-   [Patent Document 7] U.S. Patent Application Publication 2002/110735-   [Patent Document 8] Japanese Patent Application Publication    H07-302614-   [Patent Document 9] Japanese Patent Application Publication    2003-272700

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a nonaqueouselectrolytic solution having excellent battery characteristics such aselectrical capacity, cycle property and storage property and capable ofmaintaining the excellent battery characteristics for a long time, andto provide a lithium secondary battery using the nonaqueous electrolyticsolution.

The present inventors have found that incorporation of a specificethylene carbonate derivative together with (A) a triple bond-containingcompound and/or (B) a pentafluorophenyloxy compound into a nonaqueouselectrolytic solution in a specific proportion can reduce generation ofa gas and can maintain the battery performance such as cycle propertyfor a long time, and have completed the present invention.

Thus, the present invention provides the following (1) and (2):

(1) A nonaqueous electrolytic solution for a lithium secondary battery,in which an electrolyte salt is dissolved in a nonaqueous solvent,comprising 0.1 to 10% by weight of an ethylene carbonate derivativerepresented by the following general formula (I):

wherein R¹ to R³ each independently represents a hydrogen atom, ahalogen atom, a C₂ to C₁₂ alkenyl group, a C₂ to C₁₂ alkynyl group or aC₆ to C₁₈ aryl group, provided that ethylene carbonate is excluded fromthe definition of the ethylene carbonate derivative, and 0.01 to 10% byweight of (A) a triple bond-containing compound and/or (B) apentafluorophenyloxy compound represented by the following generalformula (X):

wherein R¹⁵ represents a C₂ to C₁₂ alkylcarbonyl group, a C₂ to C₁₂alkoxycarbonyl group, a C₇ to C₁₈ aryloxycarbonyl group or a C₁ to C₁₂alkanesulfonyl group with the proviso that at least one of the hydrogenatoms of R¹⁵ may be each substituted with a halogen atom or a C₆ to C₁₈aryl group.(2) A lithium secondary battery comprising a positive electrode, anegative electrode, and a nonaqueous electrolytic solution whichincludes an electrolyte salt dissolved in a nonaqueous solvent, whereinthe nonaqueous electrolytic solution comprising 0.1 to 10% by weight ofan ethylene carbonate derivative represented by the above generalformula (I), and 0.01 to 10% by weight of (A) a triple bond-containingcompound and/or (B) a pentafluorophenyloxy compound represented by theabove general formula (X).

Since the nonaqueous electrolytic solution of the present invention isfree of generation of a gas therein and liquid exhaustion phenomenon,the battery characteristics of the lithium secondary battery such aselectrical capacity, cycle property and storage property can be improvedand maintained for a long time.

The lithium secondary battery using the nonaqueous electrolytic solutionof the present invention shows excellent battery characteristics such aselectrical capacity, cycle property and storage property and can exhibitthe excellent battery performance for a long time.

BEST MODE FOR CARRYING OUT THE INVENTION

The nonaqueous electrolytic solution for a lithium secondary batteryaccording to the present invention, in which an electrolyte salt isdissolved in a nonaqueous solvent, is characterized in that thenonaqueous electrolytic solution comprises 0.1 to 10% by weight of anethylene carbonate derivative represented by the following generalformula (I) (hereinafter referred to simply as “the ethylene carbonatederivative”) and 0.01 to 10% by weight of (A) a triple bond-containingcompound and/or (B) a pentafluorophenyloxy compound represented by thefollowing general formula (X) (hereinafter referred to simply as “thepentafluorophenyloxy compound”).

It is considered that the conjoint use of the ethylene carbonatederivative and (A) the triple bond-containing compound and/or (B) thepentafluorophenyloxy compound permits the formation of a strong coatingover a negative electrode, so that the decomposition of the solvent canbe prevented and the battery characteristics such as electricalcapacity, cycle property and storage property can be improved.

The ethylene carbonate derivative used in the present invention isrepresented by the following general formula (I):

wherein R¹ to R³ each independently represents a hydrogen atom, ahalogen atom, a C₂ to C₁₂ alkenyl group, a C₂ to C₁₂ alkynyl group or aC₆ to C₁₈ aryl group, provided that ethylene carbonate is excluded fromthe definition of the ethylene carbonate derivative.

Examples of the halogen atom include a fluorine, chlorine, bromine andiodine atom. Of these atoms, fluorine and chlorine atoms are preferred.A fluorine atom is particularly preferred.

Examples of the C₂ to C₁₂ alkenyl group include a vinyl group, an allylgroup and a crotyl group. A C₂ to C₅ alkenyl group is preferred. A vinylgroup is particularly preferred.

Examples of suitable C₂ to C₁₂ alkynyl group include C₂ to C₅ alkynylgroups such as ethynyl group, 2-propynyl group, 3-butynyl group and1-methyl-2-propynyl group.

Examples of C₆ to C₁₈ aryl group include a phenyl group, a tolyl group,a xylyl group and a naphthyl group.

Specific examples of the ethylene carbonate derivative includefluoroethylene carbonate (FEC), vinylethylene carbonate (VEC),4,5-divinyl-1,3-dioxolan-2-one, 4-methyl-5-vinyl-1,3-dioxolan-2-one,4-ethyl-5-vinyl-1,3-dioxolan-2-one, 4-propyl-5-vinyl-1,3-dioxolan-2-one,4-butyl-5-vinyl-1,3-dioxolan-2-one, 4-pentyl-5-vinyl-1,3-dioxolan-2-one,4-hexyl-5-vinyl-1,3-dioxolan-2-one, 4-phenyl-5-vinyl-1,3-dioxolan-2-one,4,4-difluoro-1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one.

In the present specification, when isomers are possible, the compoundmay be used as either single isomer or as the combined mixture. The sameapplies to the rest of the specification.

Of these ethylene carbonate derivatives, at least one compound selectedfrom FEC, VEC, 4,5-divinyl-1,3-dioxolan-2-one and4,5-difluoro-1,3-dioxolan-2-one is preferred. Use of FEC and/or VEC isparticularly preferred for reasons of improved charging and dischargingcharacteristics and prevention of gas generation.

When the amount of the ethylene carbonate derivative contained in thenonaqueous electrolytic solution is excessively small, the desiredbattery performance may not be obtained. When excessively large, on theother hand, the battery performance is occasionally reduced. Thus, theamount is 0.1 to 10% by weight, preferably 0.5 to 5% by weight, morepreferably 1 to 3% by weight, based on the weight of the nonaqueouselectrolytic solution.

As the triple bond-containing compound used in the present invention,one or more alkyne derivatives represented by the following generalformulas (II) to (VII) are preferable.

In the formulas (II) to (V), R⁴ to R¹⁰ each independently represents ahydrogen atom, a C₁ to C₁₂, preferably C₁ to C₅ alkyl group, a C₃ to C₆cycloalkyl group or a C₆ to C₁₂ aryl group. R⁵ and R⁶, and R⁷ and R⁸ maybe taken in combination to each other to represent a C₃ to C₆ cycloalkylgroup. Y¹ and Y² may be the same or different and each represents—COOR¹⁶, —COR¹⁰ or SO₂R¹⁰, and x represents an integer of 1 or 2.

In the formula (VI), R¹¹ to R¹³ each independently represents a hydrogenatom, a C₁ to C₁₂, preferably C₁ to C₅ alkyl group, a C₃ to C₆cycloalkyl group, a C₆ to C₁₂ aryl group or a C₇ to C₁₂ aralkyl group,or R¹² and R¹³ may be taken in combination to represent a C₃ to C₆cycloalkyl group, W represents a sulfoxide group, a sulfone group or anoxalyl group, Y³ represents a C₁ to C₁₂ alkyl, alkenyl or alkynyl group,a C₃ to C₆ cycloalkyl group, a C₆ to C₁₂ aryl group or a C₇ to C₁₂aralkyl group, and x has the same meaning as above.

In the formula (VII), R⁴ has the same meaning as above, R¹⁴ represents aC₁ to C₁₂, preferably C₁ to C₅ alkyl group, a C₃ to C₆ cycloalkyl groupor a C₆ to C₁₂ aryl group, and p represents an integer of 1 or 2.

Specific examples of the alkyne derivative represented by the generalformula (II) in which Y¹=—COOR¹⁰ and x=1 include 2-propynyl methylcarbonate [R⁴ to R⁶═H, R¹⁰=methyl group], 1-methyl-2-propynyl methylcarbonate [R⁴═R⁶═H, R⁵═R¹⁰=methyl group], 2-propynyl ethyl carbonate [R⁴to R⁶═H, R¹⁰=ethyl group], 2-propynyl propyl carbonate [R⁴ to R⁶═H,R¹⁰=propyl group], 2-propynyl butyl carbonate [R⁴ to R⁶═H, R¹⁰=butylgroup], 2-propynyl phenyl carbonate [R⁴ to R⁶═H, R¹³=phenyl group],2-propynyl cyclohexyl carbonate [R⁴ to R⁶═H, R¹⁰=cyclohexyl group],2-butynyl methyl carbonate [R⁴═R¹⁰=methyl group, R⁵═R⁶=H], 2-pentynylmethyl carbonate [R⁴=ethyl group, R⁵═R⁶═H, R¹⁰=methyl group],1-methyl-2-butynyl methyl carbonate [R⁴═R⁵=methyl group, R⁶═H,R¹⁰=methyl group], 1,1-dimethyl-2-propynyl methyl carbonate [R⁴═H,R⁵═R⁶═R¹⁰=methyl group], 1,1-diethyl-2-propynyl methyl carbonate [R⁴═H,R⁵═R⁶=ethyl group, R¹⁰=methyl group], 1-ethyl-1-methyl-2-propynyl methylcarbonate [R⁴═H, R⁵=ethyl group, R⁶═R¹⁰=methyl group],1-isobutyl-1-methyl-2-propynyl methyl carbonate [R⁴═H, R⁵=isobutylgroup, R⁶═R¹⁰=methyl group], 1,1-dimethyl-2-butynyl methyl carbonate [R⁴to R⁶═R¹⁰=methyl group], 1-ethynylcyclohexyl methyl carbonate [R⁴═H, R⁵and R⁶ are bonded to represent a pentamethylene group, R¹⁰=methylgroup], 1-phenyl-1-methyl-2-propynyl methyl carbonate [R⁴═H, R⁵=phenylgroup, R⁶═R¹⁰=methyl group], 1,1-diphenyl-2-propynyl methyl carbonate[R⁴═H, R⁵═R⁶=phenyl group, R¹⁰=methyl group] and 1,1-dimethyl-2-propynylethyl carbonate [R⁴═H, R⁵═R⁶=methyl group, R¹⁰=ethyl group].

Specific examples of the alkyne derivative represented by the generalformula (II) in which Y¹=—COR¹⁰ and x=1 include 2-propynyl formate [R⁴to R⁶═R¹⁰═H], 2-propynyl acetate [R⁴ to R⁶═H, R¹⁰=methyl group],1-methyl-2-propynyl formate [R⁴═H, R⁵=methyl group, R⁶═R¹⁰═H],1-methyl-2-propynyl acetate [R⁴═R⁶═H, R⁵═R¹⁰=methyl group], 2-propynylpropionate [R⁴ to R⁶═H, R¹⁰=ethyl group], 2-propynyl butyrate [R⁴ toR⁶═H, R¹⁰=propyl group], 2-propynyl benzoate [R⁴ to R⁶═H, R¹⁰=phenylgroup], 2-propynyl cyclohexylcarboxylate [R⁴ to R⁶═H, R¹⁰=cyclohexylgroup], 2-butynyl formate [R⁴=methyl group, R⁵═R⁶═R¹⁰═H], 3-butynylformate [R⁴ to R⁶═R¹⁰═H], 2-pentynyl formate [R⁴=ethyl group,R⁵═R⁶═R¹⁰═H], 1-methyl-2-butynyl formate [R⁴═R⁵═R¹⁰=methyl group, R⁶═H],1,1-dimethyl-2-propynyl formate [R⁴═R¹⁰═H, R⁵═R⁶=methyl group],1,1-diethyl-2-propynyl formate [R⁴═R¹⁰═H, R⁵═R⁶=ethyl group],1-ethyl-1-methyl-2-propynyl formate [R⁴═R¹⁰═H, R⁵=ethyl group, R⁶=methylgroup], 1-isobutyl-1-methyl-2-propynyl formate [R⁴═R¹⁰═H, R⁵=isobutylgroup, R⁶=methyl group], 1,1-dimethyl-2-butynyl formate [R⁴ to R⁶=methylgroup, R¹⁰═H], 1-ethynylcyclohexyl formate [R⁴═R¹⁰═H, R⁵ and R⁶ arebonded to represent a pentamethylene group],1-phenyl-1-methyl-2-propynyl formate [R⁴═R¹⁰═H, R⁵=phenyl group,R⁶=methyl group], 1,1-diphenyl-2-propynyl formate [R⁴═R¹⁰═H,R⁵═R⁶=phenyl group], 2-butynyl acetate [R³═R¹⁰=methyl group, R⁴═R⁵═H],2-pentynyl acetate [R⁴=ethyl group, R⁵═R⁶═H, R¹⁰=methyl group],1-methyl-2-butynyl acetate [R⁴═R⁵═R¹⁰=methyl group, R⁶═H],1,1-dimethyl-2-propynyl acetate [R⁴═H, R⁵═R⁶═R¹⁰=methyl group],1,1-diethyl-2-propynyl acetate [R⁴═H, R⁵═R⁶=ethyl group, R¹⁰=methylgroup], 1-ethyl-1-methyl-2-propynyl acetate [R⁴═H, R⁵=ethyl group,R⁶═R¹⁰=methyl group], 1-isobutyl-1-methyl-2-propynyl acetate [R⁴═H,R⁵=isobutyl group, R⁶═R¹⁰=methyl group], 1,1-dimethyl-2-butynyl acetate[R⁴ to R⁶=methyl group, R¹⁰=methyl group], 1-ethynylcyclohexyl acetate[R⁴═H, R⁵ and R⁶ are bonded to represent a pentamethylene group,R¹⁰=methyl group], 1-phenyl-1-methyl-2-propynyl acetate [R⁴═H, R⁵=phenylgroup, R⁶═R¹⁰=methyl group], 1,1-diphenyl-2-propynyl acetate [R⁴═H,R⁵═R⁶=phenyl group, R¹⁰=methyl group] and 1,1-dimethyl-2-propynylpropionate [R⁴═H, R⁵═R⁶=methyl group, R¹⁰=ethyl group].

Specific examples of the alkyne derivative represented by the generalformula (II) in which Y¹=—SO₂R¹⁰ and x=1 include 2-propynylmethanesulfonate [R⁴ to R⁶═H, R¹⁰=methyl group], 1-methyl-2-propynylmethanesulfonate [R⁴═R⁶═H, R⁵═R¹⁰=methyl group], 2-propynylethanesulfonate [R⁴ to R⁶═H, R¹⁰=ethyl group], 2-propynylpropanesulfonate [R⁴ to R⁶═H, R¹⁰=propyl group], 2-propynylp-toluenesulfonate [R⁴ to R⁶═H, R¹⁰=p-tolyl group], 2-propynylcyclohexylsulfonate [R⁴ to R⁶═H, R¹⁰=cyclohexyl group], 2-butynylmethanesulfonate [R⁴═R¹⁰=methyl group, R⁵═R⁶═H], 2-pentynylmethanesulfonate [R⁴=ethyl group, R⁵═R⁶═H, R¹⁰=methyl group],1-methyl-2-butynyl methanesulfonate [R⁴═R⁵═R¹⁰=methyl group, R⁶═H],1,1-dimethyl-2-propynyl methanesulfonate [R⁴═H, R⁵═R⁶═R¹⁰=methyl group],1,1-diethyl-2-propynyl methanesulfonate [R⁴═H, R⁵═R⁶=ethyl group,R¹⁰=methyl group], 1-ethyl-1-methyl-2-propynyl methanesulfonate [R⁴═H,R⁵=ethyl group, R⁶═R¹⁰=methyl group], 1-isobutyl-1-methyl-2-propynylmethanesulfonate [R⁴═H, R⁵=isobutyl group, R⁶═R¹⁰=methyl group],1,1-dimethyl-2-butynyl methanesulfonate [R⁴ to R⁶═R¹⁰=methyl group],1-ethynylcyclohexyl methanesulfonate [R⁴═H, R⁵ and R⁶ are bonded torepresent a pentamethylene group, R¹⁰=methyl group],1-phenyl-1-methyl-2-propynyl methanesulfonate [R⁴═H, R⁵=phenyl group,R⁶═R¹⁰=methyl group], 1,1-diphenyl-2-propynyl methanesulfonate [R⁴═H,R⁵═R⁶=phenyl group, R¹⁰=methyl group] and 1,1-dimethyl-2-propynylethanesulfonate [R⁴═H, R⁵═R⁶=methyl group, R¹⁰=ethyl group].

Specific examples of the alkyne derivative represented by the generalformula (II) in which x=2 include 3-butynyl methyl carbonate [R⁴ toR⁶═H, Y¹=—COOCH₃], 3-butynyl acetate [R⁴ to R⁶═H, Y¹=—COCH₃] and3-butynyl methanesulfonate [R⁴ to R⁶═H, Y¹=—SO₂CH₃].

Above all, at least one alkyne derivative selected from 2-propynylmethyl carbonate, 2-propynyl ethyl carbonate, 2-propynyl propylcarbonate, 2-propynyl formate, 2-butynyl formate, 2-propynyl acetate,2-propynyl methanesulfonate and 1-methyl-2-propynyl methanesulfonate ispreferred. Particularly preferred is at least one alkyne derivativeselected from 2-propynyl methyl carbonate, 2-propynyl formate and2-propynyl methanesulfonate.

Specific examples of the alkyne derivative represented by the generalformula (III) in which Y¹═Y²=—COOR¹⁰ and x=1 include 2-butyne-1,4-dioldimethyl dicarbonate [R⁵ to R⁸═H, R¹⁰=methyl group], 2-butyne-1,4-dioldiethyl dicarbonate [R⁵ to R⁸═H, R¹⁰=ethyl group], 3-hexyne-2,5-dioldimethyl dicarbonate [R⁵═R⁷═R¹⁰=methyl group, R⁶═R⁸═H],3-hexyne-2,5-diol diethyl dicarbonate [R⁵═R⁷=methyl group, R⁶═R⁸═H,R¹⁰=ethyl group], 2,5-dimethyl-3-hexyne-2,5-diol dimethyl dicarbonate[R⁵ to R⁸═R¹⁰=methyl group] and 2,5-dimethyl-3-hexyne-2,5-diol diethyldicarbonate [R⁵ to R⁸=methyl group, R¹⁰=ethyl group]

Specific examples of the alkyne derivative represented the generalformula (III) in which Y¹═Y²=—COR¹⁰ and x=1 include 2-butyne-1,4-dioldiformate [R⁵ to R⁸═R¹⁰═H], 2-butyne-1,4-diol diacetate [R⁵ to R⁸═H,R¹⁰=methyl group], 2-butyne-1,4-diol dipropionate [R⁵ to R⁸═H, R¹⁰=ethylgroup], 3-hexyne-2,5-diol diformate [R⁵═R⁷=methyl group, R⁶═R⁸═R¹⁰═H],3-hexyne-2,5-diol diacetate [R⁵═R⁷═R¹⁰=methyl group, R⁶═R⁸═H],3-hexyne-2,5-diol dipropionate [R⁵═R⁷=methyl group, R⁶═R⁸═H, R¹⁰=ethylgroup], 2,5-dimethyl-3-hexyne-2,5-diol diformate [R⁵ to R⁸=methyl group,R¹⁰═H], 2,5-dimethyl-3-hexyne-2,5-diol diacetate [R⁵ to R⁸═R¹⁰=methylgroup] and 2,5-dimethyl-3-hexyne-2,5-diol dipropionate [R⁵ to R⁸=methylgroup, R¹⁰=ethyl group].

Specific examples of the alkyne derivative represented by the generalformula (III) in which Y¹═Y²═—SO₂R¹⁰ and x=1 include 2-butyne-1,4-dioldimethanesulfonate [R⁵ to R⁸═H, R¹⁰=methyl group], 2-butyne-1,4-dioldiethanesulfonate [R⁵ to R⁸═H, R¹⁰=ethyl group], 3-hexyne-2,5-dioldimethanesulfonate [R⁵═R⁷═R¹⁰=methyl group, R⁶═R⁸═H], 3-hexyne-2,5-dioldiethanesulfonate [R⁵═R⁷=methyl group, R⁶═R⁸═H, R¹⁰=ethyl group],2,5-dimethyl-3-hexyne-2,5-diol dimethanesulfonate [R⁵ to R⁸═R¹⁰=methylgroup] and 2,5-dimethyl-3-hexyne-2,5-diol diethanesulfonate [R⁵ toR⁸=methyl group, R¹⁰=ethyl group]

Of the alkyne derivatives represented by the general formula (III), atleast one alkyne derivative selected from 2-butyne-1,4-diol dimethylcarbonate, 2-butyne-1,4-diol diethyl carbonate, 3-hexyne-2,5-dioldimethyl dicarbonate, 2,5-dimethyl-3-hexyne-2,5-diol dimethyldicarbonate, 2-butyne-1,4-diol diacetate, 2-butyne-1,4-diol diformate,3-hexyne-2,5-diol diformate, 2,5-dimethyl-3-hexyne-2,5-diol diformate,2-butyne-1,4-diol dimethanesulfonate, 3-hexyne-2,5-dioldimethanesulfonate and 2,5-dimethyl-3-hexyne-2,5-diol dimethanesulfonateis preferred.

Particularly preferred is at least one alkyne derivative selected from2-butyne-1,4-diol dimethyl carbonate, 2-butyne-1,4-diol diformate and2-butyne-1,4-diol dimethanesulfonate.

Specific examples of the alkyne derivative represented by the generalformula (IV) in which Y¹═Y²=—COOR¹⁰ and x=1 include2,4-hexadiyne-1,6-diol dimethyl dicarbonate [R⁵ to R⁸═H, R¹⁰=methylgroup], 2,4-hexadiyne-1,6-diol diethyl dicarbonate [R⁵ to R⁸═H,R¹⁰=ethyl group], 2,7-dimethyl-3,5-octadiyne-2,7-diol dimethyldicarbonate [R⁵ to R⁸═R¹⁰=methyl group] and2,7-dimethyl-3,5-octadiyne-2,7-diol diethyl dicarbonate [R⁵ to R⁸=methylgroup, R¹⁰=ethyl group].

Specific examples of the alkyne derivative represented by the generalformula (IV) in which Y¹═Y²=—COR¹⁰ and x=1 include2,4-hexadiyne-1,6-diol diacetate [R⁵ to R⁸═H, R¹⁰=methyl group],2,4-hexadiyne-1,6-diol dipropionate [R⁵ to R⁸═H, R¹⁰=ethyl group],2,7-dimethyl-3,5-octadiyne-2,7-diol diacetate [R⁵ to R⁸=methyl group,R¹⁰=methyl group] and 2,7-dimethyl-3,5-octadiyne-2,7-diol dipropionate[R⁵ to R⁸=methyl group, R¹⁰=ethyl group].

Specific examples of the alkyne derivative represented by the generalformula (IV) in which Y¹═Y²=—SO₂R¹⁰ and x=1 include2,4-hexadiyne-1,5-diol dimethanesulfonate [R⁵ to R⁸═H, R¹⁰=methylgroup], 2,4-hexadiyne-1,6-diol diethanesulfonate [R⁵ to R⁸═H, R¹⁰=ethylgroup], 2,7-dimethyl-3,5-octadiyne-2,7-diol dimethanesulfonate [R⁵ toR⁸═R¹⁰=methyl group] and 2,7-dimethyl-3,5-octadiyne-2,7-dioldiethanesulfonate [R⁵ to R⁸=methyl group, R¹⁰=ethyl group].

Of the alkyne derivatives represented by the general formula (IV), atleast one alkyne derivative selected from 2,4-hexadiyne-1,6-dioldimethyl dicarbonate, 2,4-hexadiyne-1,6-diol diacetate and2,4-hexadiyne-1,6-diol dimethanesulfonate is preferred.

Specific examples of the alkyne derivative represented by the generalformula (V) in which x=1 include dipropargyl carbonate [R⁵ to R¹⁰═H],di(1-methyl-2-propynyl)carbonate [R⁵═R⁷=methyl group, R⁶═R⁸ to R¹⁰═H],di(2-butynyl)carbonate [R⁵ to R⁸═H, R⁹═R¹⁰=methyl group],di(2-pentynyl)carbonate [R⁵ to R⁸═H, R⁹═R¹⁰=ethyl group],di(1-methyl-2-butynyl)carbonate [R⁵═R⁶═R⁹═R¹⁰=methyl group, R⁷═R⁸═H],2-propynyl 2-butynyl carbonate [R⁵ to R⁹═H, R¹⁰=methyl group],di(1,1-dimethyl-2-propynyl)carbonate [R⁵ to R⁸=methyl group, R⁹═R¹⁰═H],di(1,1-diethyl-2-propynyl)carbonate [R⁵ to R⁸=ethyl group, R⁹═R¹⁰═H],di(1-ethyl-1-methyl-2-propynyl)carbonate [R⁵═R⁷=ethyl group,R⁶═R⁸=methyl group, R⁹═R¹⁰═H],di(1-isobutyl-1-methyl-2-propynyl)carbonate [R⁵═R⁷=isobutyl group,R⁶═R⁸=methyl group, R⁹═R¹⁰═H], di(1,1-dimethyl-2-butynyl)carbonate [R⁵to R¹⁰=methyl group] and di(1-ethynylcyclohexyl)carbonate [R⁵ and R⁶ arebonded to represent a pentamethylene group, R⁷ and R⁸ are bonded torepresent pentamethylene group, R⁹═R¹⁰═H].

Specific examples of the alkyne derivative represented by the generalformula (V) in which x=2 include di(3-butynyl)carbonate [R⁵ to R¹⁰═H].

Of the alkyne derivatives represented by the general formula (V), atleast one alkyne derivative selected from dipropargyl carbonate,di(1-methyl-2-propynyl)carbonate and di(2-butynyl)carbonate ispreferred.

Specific examples of the alkyne derivative represented by the generalformula (VI) in which W represents a sulfoxide group and x=1 includedi(2-propynyl)sulfite [R¹¹ to R¹³═H, Y³=2-propynyl group],di(1-methyl-2-propynyl)sulfite [R¹¹═H, R¹²=methyl group, R¹³═H,Y³=1-methyl-2-propynyl group], di(2-butynyl)sulfite [R¹¹=methyl group,R¹²═R¹³═H, Y³=2-butynyl group], di(2-pentynyl)sulfite [R¹¹=ethyl group,R¹²═R¹³═H, Y³=2-pentynyl group], di(1-methyl-2-butynyl)sulfite[R¹¹═R¹²=methyl group, R¹³═H, Y³=1-methyl-2-butynyl group],di(1,1-dimethyl-2-propynyl)sulfite [R¹¹═H, R¹²═R¹³=methyl group,Y³=1,1-dimethyl-2-propynyl group], di(1,1-diethyl-2-propynyl)sulfite[R¹¹═H, R¹²═R¹³=ethyl group, Y³=1,1-diethyl-2-propynyl group],di(1-ethyl-1-methyl-2-propynyl)sulfite [R¹¹═H, R¹²=ethyl group,R¹³=methyl group, Y³=1-ethyl-1-methyl-2-propynyl group],di(1-isobutyl-1-methyl-2-propynyl)sulfite [R¹¹═H, R¹²=isobutyl group,R¹³=methyl group, Y³=1-isobutyl-1-methyl-propynyl group],di(1,1-dimethyl-2-butynyl)sulfite [R¹¹═R¹²═R¹³=methyl group,Y³=1,1-dimethyl-2-butynyl group], di(1-ethynylcyclohexyl)sulfite [R¹¹═H,R¹² and R¹³ are combined to represent pentamethylene group,Y³=1-ethynylcyclohexyl group], di(1-methyl-1-phenyl-2-propynyl)sulfite[R¹¹═H, R¹²=phenyl group, R¹³=methyl group,Y³=1-methyl-1-phenyl-2-propynyl group],di(1,1-diphenyl-2-propynyl)sulfite [R¹¹═H, R¹²═R¹³=phenyl group,Y³=1,1-diphenyl-2-propynyl group], methyl 2-propynyl sulfite [R¹¹ toR¹³═H, Y³=methyl group], methyl 1-methyl-2-propynyl sulfite [R¹¹═H,R¹²=methyl group, R¹³═H, Y³=methyl group], ethyl 2-propynyl sulfite [R¹¹to R¹³═H, Y³=ethyl group], phenyl 2-propynyl sulfite [R¹¹ to R¹³═H,Y³=phenyl group] and cyclohexyl 2-propynyl sulfite [R¹¹ to R¹³═H,Y³=cyclohexyl group].

Specific examples of the alkyne derivative represented by the generalformula (VI) in which W represents a sulfoxide group and x=2 includedi(3-butynyl)sulfite [R¹¹ to R¹³═H, Y³=3-butynyl group].

Of the alkyne derivatives represented by the general formula (VI), atleast one alkyne derivative selected from di(2-propynyl)sulfite,di(1-methyl-2-propynyl)sulfite, di(2-butynyl)sulfite, methyl 2-propynylsulfite, methyl 1-methyl-2-propynyl sulfite and ethyl 2-propynyl sulfiteis preferred. Particularly preferred is at least one ofdi(2-propynyl)sulfite, methyl-2-propynyl sulfite and ethyl 2-propynylsulfite.

Specific examples of the alkyne derivative of the general formula (VI)in which W represents a sulfone group and x=1 includedi(2-propynyl)sulfate [R¹¹ to R¹³═H, Y³=2-propynyl group],di(1-methyl-2-propynyl)sulfate [R¹¹═R¹³═H, R¹²=methyl group,Y³=1-methyl-2-propynyl group], di(2-butynyl)sulfate [R¹¹=methyl group,R¹²═R¹³═H, Y³=2-butynyl group], di(2-pentynyl)sulfate [R¹¹=ethyl group,R¹³═H, Y³=2-pentynyl group], di(1-methyl-2-butynyl)sulfate [R¹¹═R¹³═H,R¹²=methyl group, R¹³═H, Y³=1-methyl-2-butynyl group],di(1,1-dimethyl-2-propynyl)sulfate [R¹¹═H, R¹²═R¹³=methyl group,Y³=1,1-dimethyl-2-propynyl group], di(1,1-diethyl-2-propynyl)sulfate[R¹¹═H, R¹²═R¹³=ethyl group, Y³=1,1-diethyl-2-propynyl group],di(1-ethyl-1-methyl-2-propynyl)sulfate [R¹¹═H, R¹²=ethyl group,R¹³=methyl group, Y³=1-ethyl-1-methyl-2-propynyl group],di(1-isobutyl-1-methyl-2-propynyl)sulfate [R¹¹═H, R¹²=isobutyl group,R¹³=methyl group, Y³=1-isobutyl-1-methyl-2-propynyl group],di(1,1-dimethyl-2-butynyl)sulfate [R¹¹ to R¹³=methyl group,Y³=1,1-dimethyl-2-butynyl group], di(1-ethynylcyclohexyl)sulfate [R¹¹═H,R¹² and R¹³ are bonded to represent a pentamethylene group,Y³=1-ethynylcyclohexyl group], di(1-methyl-1-phenyl-2-propynyl)sulfate[R¹¹═H, R¹²=phenyl group, R¹³=methyl group,Y³=1-methyl-1-phenyl-2-propynyl group],di(1,1-diphenyl-2-propynyl)sulfate [R¹¹═H, R¹²═R¹³=phenyl group,Y³=1,1-diphenyl-2-propynyl group], methyl 2-propynyl sulfate [R¹¹ toR¹³═H, Y³=methyl group], methyl 1-methyl-2-propynyl sulfate [R¹¹═R¹³═H,R¹²=methyl group, Y³=methyl group], ethyl 2-propynyl sulfate [R¹¹ toR¹³═H, Y³=ethyl group], phenyl 2-propynyl sulfate [R¹¹ to R¹³═H,Y³=phenyl group] and cyclohexyl 2-propynyl sulfate [R¹¹ to R¹³═H,Y³=cyclohexyl group].

Specific examples of the alkyne derivative represented by the generalformula (VI) in which W represents a sulfone group and x=2 includedi(3-butynyl)sulfate [R¹¹ to R¹³═H, Y³=3-butynyl group].

Of the alkyne derivatives represented by the general formula (VI), atleast one alkyne derivative selected from di(2-propynyl)sulfate,di(1-methyl-2-propynyl)sulfate, methyl 2-propynyl sulfate, and ethyl2-propynyl sulfate is preferred.

Specific examples of the alkyne derivative of the general formula (VI)in which W represents an oxalyl group and x=1 includedi(2-propynyl)oxalate [R¹¹ to R¹³═H, Y³=2-propynyl group],di(1-methyl-2-propynyl)oxalate [R¹¹═R¹³═H, R¹²=methyl group,Y³=1-methyl-2-propynyl group], di(2-butynyl)oxalate [R¹¹=methyl group,R¹²═R¹³═H, Y³=2-butynyl group], di(2-pentynyl)oxalate [R¹¹=ethyl group,R¹²═R¹³═H, Y³=2-pentynyl group], di(1-methyl-2-butynyl)oxalate[R¹¹═R¹²=methyl group, R¹³═H, Y³=1-methyl-2-butynyl group],di(1,1-dimethyl-2-propynyl)oxalate [R¹¹═H, R¹²═R¹³=methyl group,Y³=1,1-dimethyl-2-propynyl group], di(1,1-diethyl-2-propynyl)oxalate[R¹¹═H, R¹²═R¹³=ethyl group, Y³=1,1-diethyl-2-propynyl group],di(1-ethyl-1-methyl-2-propynyl)oxalate [R¹¹═H, R¹²=ethyl group,R¹³=methyl group, Y³=1-ethyl-1-methyl-2-propynyl group],di(1-isobutyl-1-methyl-2-propynyl)oxalate [R¹¹═H, R¹²=isobutyl group,R¹³=methyl group, Y³=1-isobutyl-1-methyl-2-propynyl group],di(1,1-dimethyl-2-butynyl)oxalate [R¹¹ to R¹³=methyl group,Y³=1,1-dimethyl-2-butynyl group], di(1-ethynylcyclohexyl)oxalate [R¹¹═H,R¹² and R¹³ are bonded to represent a pentamethylene group,Y³=1-ethynylcyclohexyl group], di(1-methyl-1-phenyl-2-propynyl)oxalate[R¹¹═H, R¹²=phenyl group, R¹³=methyl group,Y³=1-methyl-1-phenyl-2-propynyl group],di(1,1-diphenyl-2-propynyl)oxalate [R¹¹═H, R¹²═R¹³=phenyl group,Y³=1,1-diphenyl-2-propynyl group], methyl 2-propynyl oxalate [R¹¹ toR¹³═H, Y³=methyl group], methyl 1-methyl-2-propynyl oxalate [R¹¹═H,R¹²=methyl group, R¹³═H, Y³=methyl group], ethyl 2-propynyl oxalate [R¹¹to R¹³═H, Y³=ethyl group], ethyl 1-methyl-2-propynyl oxalate [R¹¹═R¹³═H,R¹²=methyl group, Y³=ethyl group], phenyl 2-propynyl oxalate [R¹¹ toR¹³═H, Y³=phenyl group] and cyclohexyl 2-propynyl oxalate [R¹¹ to R¹³═H,Y³=cyclohexyl group].

Specific examples of the alkyne derivative represented by the generalformula (VI) in which W represents an oxalyl group and x=2 includedi(3-butynyl)oxalate [R¹¹ to R¹³═H, Y³=3-butynyl group].

Of the alkyne derivatives represented by the general formula (VI), atleast one alkyne derivative selected from di(2-propynyl)oxalate,di(1-methyl-2-propynyl)oxalate, methyl 2-propynyl oxalate, ethyl2-propynyl oxalate, methyl 1-methyl-2-propynyl oxalate and ethyl1-methyl-2-propynyl oxalate is preferred. Particularly preferred is atleast one of di(2-propynyl)oxalate, methyl-2-propynyl oxalate and ethyl2-propynyl oxalate.

Specific examples of the alkyne derivative represented by the generalformula (VII) in which p=1 include 2-pentyne [R⁴=methyl group, R¹⁴=ethylgroup], 1-hexyne [R⁴=butyl group, R¹⁴═H], 2-hexyne [R⁴=propyl group,R¹⁴=methyl group], 3-hexyne [R⁴═R¹⁴=ethyl group], 1-heptyne [R⁴=pentylgroup, R¹⁴═H], 1-octyne [R⁴=hexyl group, R¹⁴═H], 2-octyne [R⁴=methylgroup, R¹⁴=pentyl group], 4-octyne [R⁴═R¹⁴=propyl group], 1-decyne[R⁴=octyl group, R¹⁴═H], 1-dodecyne [R⁴=decyl group, R¹⁴═H],phenylacetylene [R⁴=phenyl group, R¹⁴═H], 1-phenyl-1-propyne [R⁴=phenylgroup, R¹⁴=methyl group], 1-phenyl-1-butyne [R⁴=phenyl group, R¹⁴=ethylgroup], 1-phenyl-1-pentyne [R⁴=phenyl group, R¹⁴=propyl group],1-phenyl-1-hexyne [R⁴=phenyl group, R¹⁴=butyl group], diphenylacetylene[R⁴═R¹⁴=phenyl group], 4-ethynyltoluene [R⁴=p-tolyl group, R¹⁴═H],4-tert-butylphenylacetylene [R⁴=4-tert-butylphenyl group, R¹⁴═H],1-ethynyl-4-fluorobenzene [R⁴=p-fluorophenyl group, R¹⁴═H],1,4-diethynylbenzene [R⁴=p-ethynylphenyl group, R¹⁴═H] anddicyclohexylacetylene [R⁴═R¹⁴=cyclohexyl group].

Specific examples of the alkyne derivative represented by the generalformula (VII) in which p=2 include 1,4-diphenylbutadiyne [R⁴═R¹⁴=phenylgroup].

Of the alkyne derivatives represented by the general formula (VII), atleast one alkyne derivative selected from phenylacetylene,1-phenyl-1-propyne, 1-phenyl-1-butyne, diphenylacetylene,4-ethynyltoluene, 1-ethynyl-4-fluorobenzene and 1,4-diethynylbenzene.Particularly preferred are phenylacetylene and/or 1-phenyl-1-propyne.

Of the above-described alkyne derivatives, the most preferred compoundis at least one compound selected from 2-propynyl methyl carbonate,2-propynyl methanesulfonate (compounds represented by the generalformula (II)), 2-butyne-1,4-diol dimethyl carbonate, 2-butyne-1,4-dioldiformate, 2-butyne-1,4-diol dimethanesulfonate (compounds representedby the general formula (III)), di(2-propynyl)sulfite, methyl 2-propynylsulfite, ethyl 2-propynyl sulfite, di(2-propynyl)oxalate, methyl2-propynyl oxalate and ethyl 2-propynyl oxalate (compounds representedby the general formula (VI)). Use of these alkyne compounds inconjunction with an ethylene carbonate derivative is most effective forthe improvement of charging and discharging characteristics as well asbattery characteristics such as prevention of gas generation.

When the content of at least one alkyne derivative represented by thegeneral formulas (II) to (VII) in a nonaqueous electrolytic solution isexcessively small, a satisfactory coating is not formed and, therefore,the desired battery characteristics cannot be obtained. When the contentis excessively large, the conductivity of the electrolytic solution maybe apt to be changed to cause deterioration of the batterycharacteristics. Thus, the content is 0.01 to 10% by weight, preferably0.05 to 5% by weight, more preferably 0.1 to 3% by weight, based on theweight of the nonaqueous electrolytic solution.

The mixing ratio [(the ethylene carbonate derivative):(the alkynederivative)] (weight ratio) of the ethylene carbonate derivative to thealkyne derivative is 96:4 to 25:75, preferably 90:10 to 40:60, morepreferably 80:20 to 50:50.

The pentafluorophenyloxy compound used in the present invention isrepresented by the following general formula (X):

In the formula (X), R¹⁵ represents a C₂ to C₁₂, preferably C₂ to C₅alkylcarbonyl group, a C₂ to C₁₂, preferably C₂ to C₅ alkoxycarbonylgroup, a C₇ to C₁₈ aryloxycarbonyl group or a C₁ to C₁₂, preferably C₂to C₅ alkanesulfonyl group with the proviso that at least one of thehydrogen atoms of R¹⁵ may be each substituted with a halogen atom or aC₆ to C₁₆ aryl group.

As the C₂ to C₁₂ alkylcarbonyl group, there may be mentioned linearsubstituents such as a methylcarbonyl group, an ethylcarbonyl group, apropylcarbonyl group, a butylcarbonyl group, a pentylcarbonyl group, ahexylcarbonyl group, a heptylcarbonyl group, an octylcarbonyl group, anonylcarbonyl group, a decylcarbonyl group and a dodecylcarbonyl group,and branched alkylcarbonyl groups such as an isopropylcarbonyl group, atert-butylcarbonyl group and a 2-ethylhexylcarbonyl group.

Specific examples of alkylcarbonyl groups having at least one hydrogenatom substituted with a halogen atom or a C₆ to C₁₈ aryl group include atrifluoromethylcarbonyl group, a 1,2-dichloroethylcarbonyl group, apentafluoroethylcarbonyl group, a heptafluoropropylcarbonyl group and abenzylcarbonyl group. There may be also mentioned an alkylcarbonyl grouphaving a substituent of an unsaturated bond-containing alkyl group suchas methylene group (CH₂═) and an allyl group (CH₂═CH—CH₂—). Specificexamples of the substituted alkylcarbonyl group include a vinylcarbonylgroup and 1-methylvinylcarbonyl group.

Specific examples of such a pentafluorophenyloxy compound includepentafluorophenyl acetate, pentafluorophenyl propionate,pentafluorophenyl butanoate, pentafluorophenyl trifluoroacetate,pentafluorophenyl pentafluoropropionate, pentafluorophenyl acrylate andpentafluorophenyl methacrylate. Above all, pentafluorophenyl acetate andpentafluorophenyl trifluoroacetate are preferred.

As the C₂ to C₁₂ alkoxycarbonyl group, there may be mentioned linearsubstituents such as a methoxycarbonyl group, an ethoxycarbonyl group, apropoxycarbonyl group, a butoxycarbonyl group, a pentyloxycarbonylgroup, a hexyloxycarbonyl group, a heptyloxycarbonyl group, anoctyloxycarbonyl group, a nonyloxycarbonyl group, a decyloxycarbonylgroup and a dodecyloxycarbonyl group, and branched alkoxycarbonyl groupssuch as an isopropoxycarbonyl group, a tert-butoxycarbonyl group and a2-ethylhexyloxycarbonyl group.

Specific examples of alkoxycarbonyl groups having at least one hydrogenatom substituted with a halogen atom or a C₆ to C₁₈ aryl group include a1-chloroethoxycarbonyl group, a 2-chloroethoxycarbonyl group, a2,2,2-trifluoroethoxycarbonyl group, a 2,2,2-trichloroethoxycarbonylgroup and a benzyloxycarbonyl group.

Specific examples of such a pentafluorophenyloxy compound include methylpentafluorophenyl carbonate, ethyl pentafluorophenyl carbonate,tert-butyl pentafluorophenyl carbonate, 9-fluorenylmethylpentafluorophenyl carbonate and 2,2,2-trifluoroethyl pentafluorophenylcarbonate. Of these compounds, methyl pentafluorophenyl carbonate, ethylpentafluorophenyl carbonate, tert-butyl pentafluorophenyl carbonate and2,2,2-trifluoroethyl pentafluorophenyl carbonate are preferred.Especially preferred is methyl pentafluorophenyl carbonate.

As the C₇ to C₁₈ aryloxycarbonyl group, there may be mentioned aphenyloxycarbonyl group and o-, m- or p-tolyloxycarbonyl groups.

Specific examples of a pentafluorophenyloxy compound having suchsubstituents include phenyl pentafluorophenyl carbonate anddipentafluorophenyl carbonate.

As the C₁ to C₁₂ alkanesulfonyl group, there may be mentioned linearsubstituents such as a methanesulfonyl group, an ethanesulfonyl group, apropanesulfonyl group, a butanesulfonyl group, a pentanesulfonyl group,a hexanesulfonyl group, a heptanesulfonyl group, an octanesulfonylgroup, a nonanesulfonyl group, a decanesulfonyl group and adodecanesulfonyl group, and branched alkanesulfonyl groups such as a2-propanesulfonyl group.

Specific examples of the alkanesulfonyl group having at least onehydrogen atom substituted with a halogen atom include atrifluoromethanesulfonyl group and a 2,2,2-trifluoroethanesulfonylgroup.

Examples of such a pentafluorophenyloxy compound includepentafluorophenyl methanesulfonate, pentafluorophenyl ethanesulfonate,pentafluorophenyl propanesulfonate, pentafluorophenyltrifluoromethanesulfonate and pentafluorophenyl2,2,2-trifluoroethanesulfonate. Of these, pentafluorophenylmethanesulfonate, pentafluorophenyl ethanesulfonate, pentafluorophenyltrifluoromethanesulfonate and pentafluorophenyl2,2,2-trifluoroethanesulfonate are preferred. Especially preferred arepentafluorophenyl methanesulfonate and pentafluorophenyltrifluoromethanesulfonate.

When the content of the pentafluorophenyloxy compound in a nonaqueouselectrolytic solution is excessively small, a satisfactory coating isnot formed and, therefore, the desired battery characteristics cannot beobtained. When the content is excessively large, the conductivity of theelectrolytic solution may be apt to be changed to cause deterioration ofthe battery characteristics. Thus, the content is 0.01 to 10% by weight,preferably 0.05 to 5% by weight, more preferably 0.1 to 3% by weight,based on the weight of the nonaqueous electrolytic solution.

The mixing ratio [(the pentafluorophenyloxy compound):(the ethylenecarbonate derivative)] (weight ratio) of the pentafluorophenyloxycompound to the ethylene carbonate derivative is 2:98 to 95:5,preferably 20:80 to 75:25, more preferably 30:70 to 50:50.

[Nonaqueous Solvent]

As the nonaqueous solvent used in the present invention, there may bementioned, for example, cyclic carbonates, linear carbonates, esters,sulfur acid esters, ethers, amides, phosphoric esters, sulfones,lactones, nitriles, etc.

As the cyclic carbonate, there may be mentioned EC, PC, butylenecarbonate, etc. Particularly, it is most preferred that the solventcontain EC having a high dielectric constant.

As the linear carbonate, there may be mentioned asymmetric carbonatessuch as methyl ethyl carbonate (MEC), methyl propyl carbonate, methylbutyl carbonate and ethyl propyl carbonate; and symmetric carbonatessuch as dimethyl carbonate (DMC) and diethyl carbonate (DEC). Asymmetriccarbonates which have a low melting point and are effective to obtainlow temperature characteristics of batteries are particularly preferred.MEC is most preferred among them.

As the ester, there may be mentioned methyl propionate, methyl pivalate,butyl pivalate, hexyl pivalate and octyl pivalate, etc. As the sulfuracid ester, there may be mentioned 1,3-propanesultone, 1,4-butanedioldimethanesulfonate, glycol sulfite, propylene sulfite, glycol sulfate,propylene sulfate, etc.

As the ether, there may be mentioned tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane,1,2-dibutoxyethane, etc. There may be mentioned dimethylformamide, etc.as the amide; trimethyl phosphate, trioctyl phosphate, etc. as thephosphoric ester; divinylsulfone, etc. as the sulfone; γ-butyrolactone,etc. as the lactone; and acetonitrile, adiponitrile, etc. as thenitrile.

Of the above-described nonaqueous solvents, cyclic carbonates, linearcarbonates, esters and sulfur acid esters are preferred. These solventsmay be used singly or in arbitrary combination of two or more thereof.Especially preferred is a nonaqueous solvent containing a cycliccarbonate and/or a linear carbonate.

Concretely, a combination of a cyclic carbonate such as EC and PC and alinear carbonate such as MEC and DEC is particularly preferred.

The proportion of the cyclic carbonate and the linear carbonate ispreferably such that the volume ratio [(the cyclic carbonate):(thelinear carbonate)] of the cyclic carbonate to the linear carbonate is10:90 to 40:60, preferably 20:80 to 40:60, more preferably 25:75 to45:55.

Further, it is preferred that a sulfur acid ester compound and/ordivinylsulfone be used together with a cyclic carbonate and a linearcarbonate. Particularly, it is most preferable to use divinylsulfonetogether with at least one sulfur acid ester compound selected from1,3-propanesultone, glycol sulfite and 1,4-butanediol dimethanesulfonatefor reasons of good charging and discharging characteristics.

[Electrolyte Salts]

As the electrolyte salt used in the present invention, there may bementioned, for example, LiPF₆, LiBF₄, LiClO₄, LiN(SO₂CF₃)₂,LiN(SO₂C₂F₅)₂, LiC(SO₂CF₃)₃, LiPF₄ (CF₃)₂, LiPF₃ (C₂F₆)₃, LiPF₃(CF₃)₃,LiPF₃ (iso-C₃F₇)₃ and LiPF₅ (iso-C₃F₇). Above all, particularlypreferable electrolyte salts are LiPF₆, LiBF₄ and LiN(SO₂CF₃)₂, and themost preferable electrolyte salt is LiPF₆. These electrolyte salts maybe employed singly or in combination of two or more thereof.

As the preferable combination of these electrolyte salts, there may bementioned a combination of LIPF₆ and LiBF₄, a combination of LiPF₆ andLiN(SO₂CF₃)₂ and a combination of LiBF₄ and LiN(SO₂CF₃)₂. Particularlypreferred is a combination of LiPF₆ and LiBF₄.

The electrolyte salts may be mixed at any arbitrary ratio. When LiPF₆ isused in combination with other electrolyte salts, the proportion (molarratio) of said other electrolyte salts relative to all the electrolytesalts is preferably 0.01 to 45%, more preferably 0.03 to 20%, still morepreferably 0.05 to 10%, most preferably 0.05 to 5%.

All the electrolyte salts are used by dissolving in the above-describednonaqueous solvent to a concentration of generally 0.1 to 3 M,preferably 0.5 to 2.5 M, more preferably 0.7 to 2.0 M, most preferably0.8 to 1.4 M.

As a preferred combination of the above-described nonaqueous solvent andthe electrolyte salt, there may be mentioned an electrolytic solutioncomposed of a mixed solvent of (i) EC and/or PC and (ii) MEC and/or DEC,and an electrolyte salt of LiPF₆ and/or LiBF₄.

More specifically, it is preferable to combine a mixed solvent of (i) ECand/or PC and (ii) MEC and/or DEC having a volume ratio [(i):(ii)] ofpreferably 15:85 to 45:55, more preferably 20:80 to 40:60, particularlypreferably 25:75 to 35:65, with an electrolyte salt of LiPF₆. It is alsopreferable to combine the above mixed solvent with LiPF₆ and LiBF₄, orwith an electrolyte salt of LiPF₆ and LiN(SO₂CF₃)₂.

[Preparation of Nonaqueous Electrolytic Solution]

The electrolytic solution of the present invention may be obtained, forexample, by mixing the above-described nonaqueous solvents such as EC,PC and MEC, dissolving therein an electrolyte salt, and furtherdissolving therein an ethylene carbonate derivative and (A) a triplebond-containing compound such as at least one alkyne derivativerepresented by the above general formulas (II) to (VII) and/or (B) apentafluorophenyloxy compound.

In this case, it is preferred that the nonaqueous solvents, ethylenecarbonate derivatives, (A) triple bond-containing compounds and/or (B)pentafluorophenyloxy compounds, and other additives used are previouslypurified to reduce impurities as much as possible to the extent that theproductivity is not considerably deteriorated.

By incorporating, for example, air or carbon dioxide in the nonaqueouselectrolytic solution of the present invention, the generation of gasesdue to decomposition of the electrolytic solution may be prevented andthe battery characteristics such as cycle property and storage propertymay be improved.

As the method for incorporating (dissolving) carbon dioxide or air inthe nonaqueous electrolytic solution, there may be used (1) a method inwhich the nonaqueous electrolytic solution is previously contacted withair or a carbon dioxide-containing gas before the solution is poured inthe battery; or (2) a method in which after the solution has been pouredin the battery, air or a carbon dioxide-containing gas is charged in thebattery before or after sealing the battery. It is preferred that theair or carbon dioxide-containing gas contains as little moisture aspossible and have a dew point of −40° C. or below, particularlypreferably −50° C. or below.

In the nonaqueous electrolytic solution of the present invention, safetyof the battery in the case of overcharging can be ensured by furtherincorporating an aromatic compound thereinto.

As such an aromatic compound, there may be mentioned, for example, thefollowing (a) to (c):

(a) cyclohexylbenzene, a fluorocyclohexylbenzene compound(1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene,1-fluoro-4-cyclohexylbenzene), biphenyl;(b) tert-butylbenzene, 1-fluoro-4-tert-butylbenzene, tert-amylbenzene,4-tert-butylbiphenyl, 4-tert-amylbiphenyl;(c) terphenyls (o-, m- and p-), diphenyl ether, 2-fluorodiphenyl ether,4-diphenyl ether, fluorobenzene, difluorobenzenes (o-, m- and p-),2-fluorobiphenyl, 4-fluorobiphenyl, 2,4-difluoroanisole, partiallyhydrogenated terphenyls (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl,1,2-diphenylcyclohexane, o-cyclohexylbiphenyl).

Above all, (a) and (b) are preferred. Most preferred is at least onecompound selected from cyclohexylbenzene, fluorocyclohexylbenzenecompounds (1-fluoro-4-cyclohexylbenzene, etc.), tert-butylbenzene andtert-amylbenzene.

As the combination of two or more kinds of the above-described aromaticcompounds, there may be mentioned, for example, the followingcombinations (d) to (f):

(d) combination of biphenyl with tert-butyl benzene, combination ofbiphenyl with tert-amylbenzene, combination of cyclohexylbenzene withtert-amylbenzene, combination of cyclohexylbenzene with1-fluoro-4-tert-butylbenzene, and combination of tert-amylbenzene with1-fluoro-4-tert-butylbenzene,(e) combination of biphenyl with cyclohexylbenzene, and combination ofcyclohexylbenzene with tert-butylbenzene;(f) combination of biphenyl with fluorobenzene, combination ofcyclohexylbenzene with fluorobenzene, combination of 2,4-difluoroanisolewith cyclohexylbenzene, combination of cyclohexylbenzene with afluorocyclohexylbenzene compound, combination of afluorocyclohexylbenzene compound with fluorobenzene, and combination of2,4-difluoroanisole with a fluorocyclohexylbenzene compound.

Of the above combinations, those of (d) and those of (e) are preferred,and those of (d) are more preferred. Of the combinations of (d), thoseincluding a fluorine-containing compound are particularly preferred. Themixing ratio [(a fluorine-free aromatic compound):(a fluorine-containingaromatic compound)] (weight ratio) of a fluorine-free aromatic compoundto a fluorine-containing aromatic compound is preferably 50:50 to 10:90,more preferably 50:50 to 20:80, most preferably 50:50 to 25:75.

A total content of the aromatic compounds is preferably 0.1 to 5% byweight based on the weight of the nonaqueous electrolytic solution.

[Lithium Secondary Battery]

A lithium secondary battery of the present invention comprises apositive electrode, a negative electrode and a nonaqueous electrolyticsolution containing an electrolyte salt dissolved in a nonaqueoussolvent. Except for the electrolytic solution, there are no limitationswith respect to components, such as a positive electrode and a negativeelectrode. Any various known components may be used.

Thus, for example, as a positive electrode active material, a lithiumcompound metal oxide containing cobalt, manganese or nickel may be used.Such positive electrode active materials may be used singly or incombination of two or more thereof.

As the lithium compound metal oxide, there may be mentioned, forexample, LiCoO₂, LiMn₂O₄, LiNiO₂, LiCo_(1-x)Ni_(x)O₂ (0.01<x<1),LiCO_(1/3)Ni_(1/3)Mn_(1/3)O₂ and LiNi_(1/2)Mn_(3/2)O₄. These oxides maybe used in combination, such as LiCoO₂ and LiMn₂O₄, LiCoO₂ and LiNiO₂,or LiMn₂O₄ and LiNiO₂. Above all, preferably used is a lithium compoundmetal oxide, such as LiCoO₂, LiMn₂O₄ and LiNiO₂, which can be used witha charge potential of the positive electrode in a fully charged state ofat least 4.3 V on Li basis. Lithium compound metal oxides such asLiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ and LiNi_(1/2)Mn_(3/2)O₄, which are usableat 4.4 V or higher are more preferred. An element of the lithiumcompound oxides may be partly substituted with another element. Forexample, part of Co of LiCoO₂ may be substituted by Sn, Mg, Fe, Ti, Al,Zr, Cr, V, Ga, Zn, Cu or the like element.

As a positive electrode active material, a lithium-containingolivine-type phosphate may be also used. Specific examples of such aphosphate include LiFePO₄, LiCoPO₄, LiNiPO₄, LiMnPO₄,LiFe_((1-x))M_(x)PO₄ (M represents at least one member selected from Co,Ni, Mn, Cu, Zn and Cd and x is 0≦x≦0.5) and the like. Above all, LiFePO₄or LiCoPO₄ is preferably used as a positive electrode active materialfor use with a high voltage.

The lithium-containing olivine-type phosphate may be used as a mixturewith other positive electrode active material.

The conductive material for the positive electrode is not specificallylimited as long as it is an electron conductive material which does notundergo a chemical change. Examples of the conductive material includegraphites, such as natural graphite (scaly graphite, etc.) andartificial graphite, and carbon blacks, such as acetylene black, ketjenblack, channel black, furnace black, lamp black and thermal black. Thegraphites and carbon blacks may be used as an appropriate mixture. Theamount of the conductive material added to the positive electrodemixture is preferably 1 to 10% by weight, particularly preferably 2 to5% by weight.

The positive electrode may be manufactured by kneading a positiveelectrode active material, a conductive material such as acetylene blackor carbon black, and a binder such as polytetrafluoroethylene,polyvinylidene fluoride, a styrene-butadiene copolymer, anacrylonitrile-butadiene copolymer, carboxymethyl cellulose and anethylene-propylene-diene terpolymer to obtain a positive electrodemixture, then rolling the positive electrode material on a collectorsuch as an aluminum foil and a lath board made of a stainless steel, andthen subjecting the resulting assembly to a heat treatment at atemperature of about 50 to 250° C. for about 2 hours under vacuum.

As the negative electrode (negative electrode active material), theremay be used a lithium metal, a lithium alloy, a carbon material capableof occluding and releasing lithium (thermally decomposed carbonmaterials, cokes, graphites (such as artificial graphite and naturalgraphite), fired organic polymer bodies, and carbon fibers), tin, a tincompound, silicon or a silicon compound. These materials may be usedsingly or in combination of two or more thereof. At least part of thecarbon material may be replaced with tin, a tin compound, silicon or asilicon compound so that the battery capacity can be increased.

Above all, a carbon material is preferred. More preferred is a carbonmaterial having a graphite crystal structure in which the latticespacing (d₀₀₂) of the lattice face (002) is 0.340 nm or less,particularly 0.335 to 0.340 nm.

The negative electrode may be manufactured in the same manner as themethod for the manufacture of the above-described positive electrodeusing similar binder and high boiling point solvent.

There are no specific limitations with respect to the structure of thelithium secondary battery. The secondary battery may be a coin-shapedbattery, a cylindrical battery, a square-shaped battery or alaminate-type battery, each having a single layered or multi-layeredseparator.

As a separator for batteries, there can be used a single layered orlaminated porous film, woven fabric or non-woven fabric of a polyolefinsuch as polypropylene and polyethylene.

When an air permeability of a separator for batteries is excessivelylow, the mechanical strength thereof is reduced, and when it isexcessively high, the lithium ion conductivity is lowered and,therefore, the function thereof as a battery separator is insufficient,though the influence of air permeability may vary depending upon themanufacturing conditions for the separator. Thus, the air permeabilityis preferably 50 to 1000 seconds/100 cc, more preferably 100 to 800seconds/100 cc, most preferably 300 to 500 seconds/100 cc. The porosityof the separator is preferably 30 to 60%, more preferably 35 to 55%,most preferably 40 to 50% for the reason of improvement of capacitycharacteristics of the battery.

The thickness of the separator for batteries is preferably 5 to 50 μm,more preferably 10 to 40 μm, most preferably 15 to 25 μm, sincesatisfactory mechanical strength is ensured and since a higher energydensity is obtainable.

In the present invention, it is preferable to control the density of theelectrode material layers so as to increase the effect of addition of anethylene carbonate derivative and (A) a triple bond-containing compoundand/or (B) a pentafluorophenyloxy compound. In particular, the densityof the positive electrode mixture layer formed on an aluminum foil ispreferably 3.2 to 4.0 g/cm³, more preferably 3.3 to 3.9 g/cm³, mostpreferably 3.4 to 3.8 g/cm³. It may be practically difficult tomanufacture a positive electrode mixture layer with a density in excessof 4.0 g/cm³. On the other hand, the density of the negative electrodemixture layer formed on a copper foil is preferably 1.3 to 2.0 g/cm³,more preferably 1.4 to 1.9 g/cm³, most preferably 1.5 to 1.8 g/cm³. Itmay be practically difficult to manufacture a negative electrode mixturelayer with a density in excess of 2.0 g/cm³.

When the thickness of the electrode layer is excessively small, theamount of the active material in the electrode material layer isdecreased and, thus, the battery capacity is lowered. When the thicknessis excessively large, the cycle property and rate characteristics areundesirably lowered. Therefore, the thickness of the electrode layer ofthe positive electrode (per one side of the collector) is generally 30to 120 μm, preferably 50 to 100 μm. The thickness of the electrode layerof the negative electrode (per one side of the collector) is generally 1to 100 μm, preferably 3 to 70 μm.

The lithium secondary battery of the present invention shows a goodcycle property for a long period of time even when the final voltage ofcharge is 4.2 V or higher, particularly 4.3 V or higher. Further, thegood cycle property is expected even when the final voltage of charge is4.4 V or higher. The final voltage of discharge can be set to 2.5 V orhigher, and further to 2.8 V or higher. There is no specific limitationwith respect to a current value, but a constant current discharge at 0.1to 3 C is generally adopted. The lithium secondary battery of thepresent invention may be charged and discharged at −40 to 100° C.,preferably 0 to 80° C.

In the present invention, as a measure against an increase of theinternal pressure of the lithium secondary battery, a relief valve maybe provided on a sealing plate. Else, there may be adopted a method inwhich a cut is formed in a battery can, gasket or other parts.

In the lithium secondary battery of the present invention, a pluralnumber of the lithium secondary batteries may be accommodated in abattery pack in series and/or in parallel, as necessary. It is preferredthat such a battery pack is provided with at least one of a overcurrentprotection element, such as a PTC element, a thermal fuse and a bimetal,as well as a safety circuit (a circuit having a function of monitoringthe voltage, temperature, current, etc. of each battery and/or theentire battery pack and shutting off the current, as necessary).

EXAMPLES

The present invention will be described below with reference to Examplesand Comparative Examples concerning cylindrical batteries. It should benoted, however, that the present invention is not limited to theseExamples, in particular, to the combinations of solvents, etc.

Example 1 [Preparation of Nonaqueous Electrolytic Solution]

A nonaqueous solvent of EC:MEC:DEC=3:4:3 (volume ratio) was prepared, inwhich LiPF₆ as an electrolyte salt was dissolved to a concentration of 1M to obtain a nonaqueous electrolytic solution. To the nonaqueouselectrolytic solution were added fluoroethylene carbonate (FEC) to aconcentration of 2% by weight and, further, 2-propynyl methyl carbonateas an alkyne derivative to a concentration of 1% by weight based on thefinal nonaqueous electrolytic solution.

[Manufacture of Lithium Secondary Battery and Measurement of BatteryCharacteristics]

Ninety-four % by weight of LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ (positiveelectrode active material), 3% by weight of acetylene black (conductivematerial) and 3% by weight of polyvinylidene fluoride (binder) weremixed, to which 1-methyl-2-pyrrolidone as a solvent was further addedand mixed. The resulting mixture was applied onto an aluminum foil,dried, compression molded and heat treated to prepare a positiveelectrode. On the other hand, 95% by weight of artificial graphite(negative electrode active material) were mixed with 5% by weight ofpolyvinylidene fluoride (binder), to which 1-methyl-2-pyrrolidone as asolvent was further mixed. The resulting mixture was applied onto acopper foil, dried, compression molded and heat treated to prepare anegative electrode.

A cylindrical battery of an 18650 size (diameter: 18 mm, height: 65 mm)was then manufactured by using a microporous polyethylene film separator(thickness: 20 μm), pouring the above electrolytic solution and thentrapping air having a dew point of −60° C. before sealing the battery.The battery was provided with a pressure release vent and an internalcurrent breaker (PTC element). At this time, the positive electrode hadan electrode density of 3.5 g/cm³, while the negative electrode had anelectrode density of 1.6 g/cm³. The electrode layer of the positiveelectrode had a thickness (per one side of the collector) of 70 μm,while the electrode layer of the negative electrode had a thickness (perone side of the collector) of 60 μm.

The thus obtained 18650 battery was charged at a constant electriccurrent of 2.2 A (1 C) at ambient temperature (20° C.) to a voltage of4.2 V. The charging was thereafter continued for 3 hours in total undera constant voltage with a final voltage of 4.2 V. Next, the battery wasdischarged at a constant electric current of 2.2 A (1 C) to a finalvoltage of 3.0 V. The charge-discharge cycle was repeated. The initialcharge-discharge capacity was almost the same as that of a case in whichneither the ethylene carbonate derivative nor the triple bond-containingcompound was used (Comparative Example 1). The battery characteristicsafter 200 cycles were measured to reveal that the discharge capacityretention, when the initial discharge capacity was 100%, was 82.8%. Theresults are summarized in Table 1.

Examples 2 to 9

Examples 2 to 9 were conducted in the same manner as described inExample 1 except that alkyne derivatives shown in Table 1 were used inpredetermined amounts in place of 2-propynyl methyl carbonate. Theresults are also summarized in Table 1.

Example 10

Example 10 was conducted in the same manner as described in Example 1except that, after the same nonaqueous electrolytic solution as that inExample 1 had been prepared, vinylethylene carbonate (VEC) anddi(2-propynyl)sulfite were added thereto in amounts of 2% by weight and0.5% by weight, respectively, based on the final nonaqueous electrolyticsolution. The results are summarized in Table 1.

Examples 11 and 12

Examples 11 and 12 were conducted in the same manner as described inExample 1 except that the positive electrodes (positive electrode activematerials) shown in Table 1 were used in place ofLiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ and that the alkyne derivatives shown inTable 1 were used in an amount of 0.5% by weight based on the finalnonaqueous electrolytic solution. The results are summarized in Table 1.

Comparative Example 1

Comparative Example 1 was conducted in the same manner as described inExample 1 except that, after the same nonaqueous electrolytic solutionas that in Example 1 had been prepared, neither FEC nor the alkynederivative was used. The results are summarized in Table 1.

Comparative Examples 2 to 5

Comparative Examples 2 to 5 were conducted in the same manner asdescribed in Example 1 except that the conditions shown in Table 1 wereadopted for the nonaqueous electrolytic solutions. The results aresummarized in Table 1.

TABLE 1 Discharge Initial Capacity EC Composition of Discharge Retentionafter Derivative Alkyne Derivative Electrolytic Solution Capacity 200Cycles Positive Electrode (wt %) (wt %) (volume raio) (relative value)(%) Example 1 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) 2-propynyl methylcarbonate (1) 1M LiPF₆ 1.00 82.8 EC/MEC/DEC = 3/4/3 2LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) 2-propynyl methanesulfonate (1) 1MLiPF₆ 1.01 82.9 EC/MEC/DEC = 3/4/3 3 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC(2) Methyl 2-propynyl sulfite (1) 1M LiPF₆ 1.01 82.6 EC/MEC/DEC = 3/4/34 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) 2-butyne-1,4-diol dimethylcarbonate 1M LiPF₆ 1.00 81.5 (1) EC/MEC/DEC = 3/4/3 5LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) 2-butyne-1,4-dioldimethanesulfonate 1M LiPF₆ 1.00 81.7 (0.5) EC/MEC/DEC = 3/4/3 6LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) 2,4-hexadiyne-1,6-diol dimethyl 1MLiPF₆ 1.00 81.3 dicarbonate (1) EC/MEC/DEC = 3/4/3 7LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) Phenylacetylene (0.1) 1M LiPF₆ 1.0080.8 EC/MEC/DEC = 3/4/3 8 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2)Dipropargyl carbonate (0.5) 1M LiPF₆ 1.00 81.0 EC/MEC/DEC = 3/4/3 9LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) 2-propynyl formate (0.5) 1M LiPF₆1.00 80.3 EC/MEC/DEC = 3/4/3 10 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ VEC (2)Di(2-propynyl) sulfite (0.5) 1M LiPF₆ 1.00 80.7 EC/MEC/DEC = 3/4/3 11LiCo_(0.995)Zr_(0.005)O₂ FEC (2) Di(1-methyl-2-propynyl) oxalate (0.5)1M LiPF₆ 1.00 81.4 EC/MEC/DEC = 3/4/3 12 LiCoO₂ FEC (2) Ethyl 2-propynylsulfite (0.5) 1M LiPF₆ 0.98 80.5 EC/MEC/DEC = 3/4/3 Comparative 1LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ none none 1M LiPF₆ 1.00 68.4 ExampleEC/MEC/DEC = 3/4/3 2 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) none 1M LiPF₆0.99 69.7 EC/MEC/DEC = 3/4/3 3 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ VEC (2) none1M LiPF₆ 0.99 69.5 EC/MEC/DEC = 3/4/3 4 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC(2) Triphenyl phosphate (1) 1M LiPF₆ 1.00 74.3 EC/MEC/DEC = 3/4/3 5LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ none 2-propynyl methanesulfonate (1) 1MLiPF₆ 1.00 78.7 EC/MEC/DEC = 3/4/3

[Study of Proportion of Additives] Examples 13 to 16

Examples 13 to 16 were conducted in the same manner as described inExample 1 except that, after the same nonaqueous electrolytic solutionas that in Example 1 had been prepared, FEC and 2-butyne-1,4-dioldiformate as an alkyne derivative were added thereto in thepredetermined amounts shown in Table 2. The results are summarized inTable 2.

TABLE 2 Discharge Initial Capacity EC Composition of ElectrolyticDischarge Retention after Derivative Alkyne Derivative Solution Capacity200 Cycles Positive Electrode (wt %) (wt %) (volume ratio) (relativevalue) (%) Example 13 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (5)2-butyne-1,4-diol diformate (0.6) 1M LiPF₆ 1.01 81.8 EC/MEC/DEC = 3/4/314 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) 2-butyne-1,4-diol diformate (1)1M LiPF₆ 1.01 83.0 EC/MEC/DEC = 3/4/3 15 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂FEC (1) 2-butyne-1,4-diol diformate (2) 1M LiPF₆ 1.01 82.7 EC/MEC/DEC =3/4/3 16 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (1) 2-butyne-1,4-dioldiformate (3) 1M LiPF₆ 1.01 82.5 EC/MEC/DEC = 3/4/3

[Study of Proportion of Electrolyte Salts] Examples 17 to 20

Examples 17 to 20 were conducted in the same manner as described inExample 1 except that, a nonaqueous electrolytic solution was preparedby dissolving LiPF₆ and LiBF₄ as electrolyte salts to the predeterminedconcentrations shown in Table 3, and that FEC was added thereto in anamount of 2% by weight and, further, predetermined amounts of the alkynederivative as shown in Table 3 were added thereto. The results aresummarized in Table 3.

Example 21

Example 21 was conducted in the same manner as described in Example 17except that a nonaqueous electrolytic solution was prepared bydissolving LiPF₆ and LiN(SO₂CF₃)₂ as electrolyte salts to concentrationsof 0.9 M and 0.1 M, respectively, and that 2-butyne-1,4-diol diformateas an alkyne derivative was then added thereto in an amount of 1% byweight based on the final nonaqueous electrolytic solution. The resultsare summarized in Table 3.

TABLE 3 Discharge Initial Capacity EC Composition of ElectrolyticDischarge Retention after Derivative Alkyne Derivative Solution Capacity200 cycles Positive Electrode (wt %) (wt %) (volume ratio) (relativevalue) (%) Example 17 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2)Di(2-propynyl) oxalate (0.2) 0.995M LiPF₆ + 0.005M LiBF₄ 1.00 83.0EC/MEC/DEC = 3/4/3 18 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2)Di(2-propynyl) oxalate (0.2) 0.99M LiPF₆ + 0.01M LiBF₄ 1.00 83.1EC/MEC/DEC = 3/4/3 19 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2)Di(2-propynyl) oxalate (0.2) 0.95M LiPF₆ + 0.05M LiBF₄ 1.00 82.3EC/MEC/DEC = 3/4/3 20 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) Methyl2-propynyl sulfite 0.8M LiPF₆ + 0.2M LiBF₄ 1.00 82.1 (0.5) EC/MEC/DEC =3/4/3 21 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (2) 2-butyne-1,4-dioldiformate 0.9M LiPF₆ + 0.1M LiN(SO₂CF₃)₂ 1.00 82.0 (1) EC/MEC/DEC =3/4/3

[Example of Conjoint Use of Aromatic Compound] Examples 22 to 26

Examples 22 to 26 were conducted in the same manner as described inExample 1 except that di(2-propynyl)oxalate as an alkyne derivative wasused in an amount of 0.2% by weight based on the nonaqueous electrolyticsolution and, further, the predetermined amounts of ethylene carbonatederivatives and aromatic compounds shown in Table 4 were added thereto.The results are summarized in Table 4.

In Table 4, TAB means tert-amylbenzene, CHB means cyclohexylbenzene, BPmeans biphenyl, FCHB means 1-fluoro-4-cyclohexylbenzene and TBB meanstert-butylbenzene.

TABLE 4 Discharge Initial Capacity Composition of Electrolytic DischargeRetention after EC Derivative Alkyne Derivative Solution Capacity 200Cycles Positive Electrode (wt %) (wt %) (volume ratio) (relative value)(%) Example 22 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (1) Di(2-propynyl)oxalate (0.2) 1M LiPF₆ 1.01 83.9 EC/MEC/DEC = 3/4/3 + TAB 1.5 wt % + CHB1 wt % 23 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (1) Di(2-propynyl) oxalate(0.2) 1M LiPF₆ 1.00 82.8 EC/MEC/DEC = 3/4/3 + BP 0.2 wt % + CHB 3 wt %24 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (1) Di(2-propynyl) oxalate (0.2) 1MLiPF₆ 1.00 83.4 EC/MEC/DEC = 3/4/3 + CHB 1 wt % + FCHB 1 wt % 25LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (1) Di(2-propynyl) oxalate (0.2) 1MLiPF₆ 1.00 83.1 EC/MEC/DEC = 3/4/3 + TBB 2 wt % + CHB 1 wt % 26LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (1) + Di(2-propynyl) oxalate (0.2) 1MLiPF₆ 1.00 82.9 VEC (1) EC/MEC/DEC = 3/4/3 + TBB 1 wt % + BP 0.1 wt %

[Evaluation of Gas Generation] Examples 27 to 31

A cylindrical battery of an 18650 size was manufactured in the samemanner as described in Example 1 except that, after the same nonaqueouselectrolytic solution as that in Example 1 had been prepared,predetermined amounts of ethylene carbonate derivatives and alkynederivatives as shown in Table 5 were added thereto.

The thus obtained 18650 batteries were each charged at a constantelectric current of 2.2 A (1 C) at 60° C. to a voltage of 4.2 V. Thecharging was thereafter continued for 3 hours in total with a finalvoltage of 4.2 V. Next, the battery was discharged at a constantelectric current of 2.2 A (1 C) to a final voltage of 3.0 V. Thecharge-discharge cycle was repeated. The amount of a gas generated inthe batteries after 100 cycles was measured according to the Archimedesmethod. The results are summarized in Table 5.

Comparative Examples 6 to 8

Comparative Examples 6 to 8 were conducted in the same manner asdescribed in Example 27 using the same nonaqueous electrolytic solutionsas those of Comparative Example 1 to 3. The results are summarized inTable 5.

TABLE 5 Composition of Amount of Gas EC Derivative Alkyne DerivativeElectrolytic Solution Generated Positive Electrode (wt %) (wt %) (volumeratio) (ml) Example 27 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC Di(2-propynyl)oxalate (0.3) 1M LiPF₆ 0.61 (2) EC/MEC/DEC = 3/4/3 28LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC 2-propynyl methyl carbonate (1) 1MLiPF₆ 0.58 (2) EC/MEC/DEC = 3/4/3 29 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC2-propynyl methanesulfonate (1) 1M LiPF₆ 0.62 (2) EC/MEC/DEC = 3/4/3 30LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ VEC Methyl 2-propynyl sulfite (1) 1M LiPF₆0.60 (2) EC/MEC/DEC = 3/4/3 31 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC (1) +2-butyne-1,4-diol diformate (1) 1M LiPF₆ 0.56 VEC (1) EC/MEC/DEC = 3/4/3Comparative 6 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ none none 1M LiPF₆ 0.71Example EC/MEC/DEC = 3/4/3 7 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ FEC none 1MLiPF₆ 1.03 (2) EC/MEC/DEC = 3/4/3 8 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ VECnone 1M LiPF₆ 1.12 (2) EC/MEC/DEC = 3/4/3

Example 32 [Preparation of Nonaqueous Electrolytic Solution]

A nonaqueous solvent of EC:MEC:DEC=3:4:3 (volume ratio) was prepared, inwhich LiPF₆ as an electrolyte salt was dissolved to a concentration of 1M to obtain a nonaqueous electrolytic solution. To the nonaqueouselectrolytic solution were added fluoroethylene carbonate (FEC) to aconcentration of 2% by weight and, further, pentafluorophenylmethanesulfonate to a concentration of 1% by weight based on the finalnonaqueous electrolytic solution.

[Manufacture of Lithium Secondary Battery and Measurement of BatteryCharacteristics]

A cylindrical battery of an 18650 size (diameter: 18 mm, height: 65 mm)was manufactured in the same manner as described in Example 1.

The thus obtained 18650 battery was charged at a constant electriccurrent of 2.2 A (1 C) at ambient temperature (20° C.) to a voltage of4.2 V. The charging was thereafter continued for 3 hours in total undera constant voltage with a final voltage of 4.2 V. Next, the battery wasdischarged at a constant electric current of 2.2 A (1 C) to a finalvoltage of 3.0 V. The charge-discharge cycle was repeated. The initialcharge-discharge capacity was almost the same as that of a case in whichneither the ethylene carbonate derivative nor the pentafluorophenyloxycompound was used (Comparative Example 9). The battery characteristicsafter 300 cycles were measured to reveal that the discharge capacityretention, when the initial discharge capacity was 100%, was 79.1%. Theresults are summarized in Table 6.

Examples 33 to 36

Examples 33 to 36 were conducted in the same manner as described inExample 32 except that the positive electrode and pentafluorophenyloxycompound shown in Table 6 were used. The results are summarized in Table6.

Comparative Example 9

Comparative Example 9 was conducted in the same manner as described inExample 32 except that, after the same nonaqueous electrolytic solutionas that in Example 32 has been prepared, neither FEC nor thepentafluorophenyloxy compound was used. The results are summarized inTable 6.

Comparative Examples 10 to 13

Comparative Examples 10 to 13 were conducted in the same manner asdescribed in Example 32 except that the conditions shown in Table 6 wereadopted for the nonaqueous electrolytic solutions. The results aresummarized in Table 6.

TABLE 6 Discharge Composition of Initial Capacity EC ElectrolyticDischarge Retention after Pentafluorophenyloxy Compound DerivativeSolution Capacity 300 Cycles Positive Electrode (wt %) (wt %) (volumeratio) (relative value) (%) Example 32 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (1) FEC (2) 1M LiPF₆ 1.01 79.1EC/MEC/DEC = 3/4/3 33 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenylacetate (1) FEC (2) 1M LiPF₆ 1.00 78.4 EC/MEC/DEC = 3/4/3 34LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Methyl pentafluorophenyl carbonate (1) FEC(2) 1M LiPF₆ 1.00 78.9 EC/MEC/DEC = 3/4/3 35 LiCo_(0.995)Zr_(0.005)O₂Pentafluorophenyl methanesulfonate (1) FEC (2) 1M LiPF₆ 1.02 80.3EC/MEC/DEC = 3/4/3 36 LiCoO₂ Pentafluorophenyl methanesulfonate (1) FEC(2) 1M LiPF₆ 0.98 80.3 EC/MEC/DEC = 3/4/3 Comparative 9LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ none none 1M LiPF₆ 1.00 63.5 ExampleEC/MEC/DEC = 3/4/3 10 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ none FEC (2) 1M LiPF₆0.99 65.1 EC/MEC/DEC = 3/4/3 11 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ none VEC(2) 1M LiPF₆ 0.99 65.9 EC/MEC/DEC = 3/4/3 12LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Triphenyl phosphate (1) FEC (2) 1M LiPF₆1.00 70.2 EC/MEC/DEC = 3/4/3 13 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (1) none 1M LiPF₆ 1.00 75.7EC/MEC/DEC = 3/4/3

[Study of Proportion of Additives] Examples 37 to 40

Examples 37 to 40 were conducted in the same manner as described inExample 32 except that, after the same nonaqueous electrolytic solutionas that in Example 32 had been prepared, FEC and pentafluorophenylmethanesulfonate were added thereto in the amounts shown in Table 7. Theresults are summarized in Table 7.

TABLE 7 Discharge Composition of Initial Capacity EC ElectrolyticDischarge Retention after Pentafluorophenyloxy Compound DerivativeSolution Capacity 300 Cycles Positive Electrode (wt %) (wt %) (volumeratio) (relative value) (%) Example 37 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (0.1) FEC 1M LiPF₆ 1.00 77.7 (5)EC/MEC/DEC = 3/4/3 38 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenylmethanesulfonate (1) FEC 1M LiPF₆ 1.00 79.1 (2) EC/MEC/DEC = 3/4/3 39LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenyl methanesulfonate (3) FEC1M LiPF₆ 1.00 78.2 (1) EC/MEC/DEC = 3/4/3 40LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenyl methanesulfonate (5) FEC1M LiPF₆ 1.00 77.1 (0.5) EC/MEC/DEC = 3/4/3

[Study of Proportion of Electrolyte Salts] Examples 41 to 44

Examples 41 to 44 were conducted in the same manner as described inExample 32 except that, a nonaqueous electrolytic solution was preparedby dissolving LiPF₆ and LiBF₄ as electrolyte salts to the predeterminedconcentrations shown in Table 8, and that FEC was added thereto in anamount of 2% by weight and, further, pentafluorophenyl methanesulfonatewas added thereto in an amount of 1% by weight based on the finalnonaqueous electrolytic solution. The results are summarized in Table 8.

Example 45

Example 45 was conducted in the same manner as described in Example 41except that a nonaqueous electrolytic solution was prepared bydissolving LiPF₆ and LiN(SO₂CF₃)₂ as electrolyte salts to concentrationsof 0.9 M and 0.1 M, respectively, and that FEC was then was addedthereto in an amount of 2% by weight and, further,pentafluorophenylmethane sulfonate was added thereto in an amount of 1%by weight based on the final nonaqueous electrolytic solution. Theresults are summarized in Table 8.

TABLE 8 Initial Discharge Discharge Capacity EC Composition ofElectrolytic Capacity Retention after Pentafluorophenyloxy CompoundDerivative Solution (relative 300 Cycles Positive Electrode (wt %) (wt%) (volume ratio) value) (%) Example 41 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (1) FEC (2) 0.99M LiPF₆ + 0.01M LiBF₄1.00 80.0 EC/MEC/DEC = 3/4/3 42 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (1) FEC (2) 0.99M LiPF₆ + 0.01M LiBF₄1.00 80.1 EC/MEC/DEC = 3/4/3 43 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (1) FEC (2) 0.95M LiPF₆ + 0.05M LiBF₄1.00 80.4 EC/MEC/DEC = 3/4/3 44 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (1) FEC (2) 0.8M LiPF₆ + 0.2M LiBF₄1.00 79.2 EC/MEC/DEC = 3/4/3 45 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (1) FEC (2) 0.9M LiPF₆ + 0.1M 1.0079.8 LiN(SO₂CF₃)₂ EC/MEC/DEC = 3/4/3

[Example of Conjoint Use of Aromatic Compound] Examples 46 to 50

Examples 46 to 50 were conducted in the same manner as described inExample 32 except that pentafluorophenyl methanesulfonate was added inan amount of 0.5% by weight based on the nonaqueous electrolyticsolution and, further, the predetermined amounts of ethylene carbonatederivatives and aromatic compounds shown in Table 9 were added thereto.The results are summarized in Table 9.

In Table 9, TAB means tert-amylbenzene, CHB means cyclohexylbenzene, BPmeans biphenyl, TBB means tert-butylbenzene and FCHB means1-fluoro-4-cyclohexylbenzene.

TABLE 9 Discharge Initial Capacity Discharge Retention EC Composition ofElectrolytic Capacity after Pentafluorophenyloxy Compound DerivativeSolution (relative 300 Cycles Positive Electrode (wt %) (wt %) (volumeratio) value) (%) Example 46 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (0.5) FEC (1) 1M LiPF₆ 1.01 81.2EC/MEC/DEC = 3/4/3 + TAB 1.5 wt % + CHB 1 wt % 47LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenyl methanesulfonate (0.5)FEC (1) 1M LiPF₆ 1.01 81.3 EC/MEC/DEC = 3/4/3 + BP 0.2 wt % + CHB 3 wt %48 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenyl methanesulfonate (0.5)FEC (1) 1M LiPF₆ 1.01 81.6 EC/MEC/DEC = 3/4/3 + TBB 1 wt % + BP 0.1 wt %49 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenyl methanesulfonate (0.5)FEC (1) 1M LiPF₆ 1.01 81.5 EC/MEC/DEC = 3/4/3 + CHB 1 wt % + FCHB 1 wt %50 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenyl methanesulfonate (0.5)FEC (1) + 1M LiPF₆ 1.01 81.1 VEC (1) EC/MEC/DEC = 3/4/3 + TBB 2 wt % +CHB 1 wt %

[Evaluation of Gas Generation] Examples 51 to 54

A cylindrical battery of an 18650 size was manufactured in the samemanner as described in Example 1 except that, after the same nonaqueouselectrolytic solution as that in Example 1 had been prepared,predetermined amounts of ethylene carbonate derivatives andpentafluorophenyloxy compound as shown in Table 10 were added thereto.

The thus obtained 18650 batteries were each charged at a constantelectric current of 2.2 A (1 C) at 60° C. to a voltage of 4.2 V. Thecharging was thereafter continued for 3 hours in total with a finalvoltage of 4.2 V. Next, the battery was discharged at a constantelectric current of 2.2 A (1 C) to a final voltage of 3.0 V. Thecharge-discharge cycle was repeated. The amount of a gas generated inthe batteries after 300 cycles was measured according to the Archimedesmethod. The results are summarized in Table 10.

Comparative Examples 14 to 16

Comparative Examples 14 to 16 were conducted in the same manner asdescribed in Example 51 using the same nonaqueous electrolytic solutionsas those of Comparative Example 9 to 11. The results are summarized inTable 10.

TABLE 10 EC Composition of Electrolytic Amount of GasPentafluorophenyloxy Compound Derivative Solution Generated PositiveElectrode (wt %) (wt %) (volume ratio) (ml) Example 51LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Pentafluorophenyl methanesulfonate (1) FEC(2) 1M LiPF₆ 0.57 EC/MEC/DEC = 3/4/3 52 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl acetate (1) FEC (2) 1M LiPF₆ 0.65 EC/MEC/DEC = 3/4/353 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ Methyl pentafluorophenyl carbonate (1)FEC (2) 1M LiPF₆ 0.64 EC/MEC/DEC = 3/4/3 54 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂Pentafluorophenyl methanesulfonate (1) VEC (2) 1M LiPF₆ 0.63 EC/MEC/DEC= 3/4/3 Comparative 14 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ none none 1M LiPF₆0.71 Example EC/MEC/DEC = 3/4/3 15 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ none FEC(2) 1M LiPF₆ 1.03 EC/MEC/DEC = 3/4/3 16 LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂none VEC (2) 1M LiPF₆ 1.12 EC/MEC/DEC = 3/4/3

INDUSTRIAL APPLICABILITY

A lithium secondary battery having excellent battery characteristicssuch as electrical capacity, cycle property and storage property andcapable of exhibiting excellent battery performances for a long time canbe obtained by using the nonaqueous electrolytic solution of the presentinvention. The obtained secondary battery may be suitably used as acylindrical battery, a square-shaped battery, a coin-shaped battery, alaminate-type battery and other types of batteries.

1-6. (canceled)
 7. A nonaqueous electrolytic solution for a lithiumsecondary battery, in which an electrolyte salt is dissolved innonaqueous solvent, comprising: an ethylene carbonate derivativerepresented by the following general formula (I):

wherein R¹ to R³ each independently represents a hydrogen atom, ahalogen atom, a C₂ to C₁₂ alkenyl group, a C₂ to C₁₂ alkynyl group or aC₆ to C₁₈ aryl group, provided that ethylene carbonate is excluded fromthe definition of the ethylene carbonate derivative; and 0.05 to 5% byweight of (B) a pentafluorophenyloxy compound represented by the generalformula (X):

wherein R¹⁵ represents a C₂ to C₁₂ alkylcarbonyl group, a C₂ to C₁₂alkoxycarbonyl group, a C₇ to C₁₈ aryloxycarbonyl group or a C₁ to C₁₂alkanesulfonyl group with the proviso that at least one of the hydrogenatoms of R¹⁵ may be each substituted with a halogen atom or a C₆ to C₁₈aryl group, wherein the mixing ratio [((B) the pentafluorophenyloxycompound):(fluoroethylene carbonate and/or vinylethylene carbonate)](weight ratio) of (B) the pentafluorophenyloxy compound tofluoroethylene carbonate and/or vinylethylene carbonate is 2:98 to 95:5.8. The nonaqueous electrolytic solution according to claim 7,comprising: the content of the ethylene carbonate derivative representedby the general formula (I) is 0.01 to 10% by weight based on the weightof the nonaqueous electrolytic solution.
 9. The nonaqueous electrolyticsolution according to claim 7, wherein the ethylene carbonate derivativerepresented by the general formula (I) comprises fluoroethylenecarbonate and/or vinylethylene carbonate.
 10. The nonaqueouselectrolytic solution according to claim 7, wherein (B) thepentafluorophenyloxy compound comprises at least one compound selectedfrom pentafluorophenyl methanesulfonate, pentafluorophenylethanesulfonate, pentafluorophenyl propanesulfonate, pentafluorophenyltrifluoromethanesulfonate and pentafluorophenyl2,2,2-trifluoroethanesulfonate.
 11. The nonaqueous electrolytic solutionaccording to claim 7, wherein the nonaqueous solvent comprises a cycliccarbonate and a linear carbonate.
 12. The nonaqueous electrolyticsolution according to claim 7, wherein the linear carbonates comprisesat least one asymmetrical carbonates selected from methyl ethylcarbonate, methyl propyl carbonate, methyl butyl carbonate and ethylpropyl carbonate.
 13. The nonaqueous electrolytic solution according toclaim 12, wherein the asymmetrical carbonate is methyl ethyl carbonate.14. The nonaqueous electrolytic solution according to claim 7, whereinthe electrolyte salt comprises LiPF₆ and other electrolyte salts, andthe proportion (molar ratio) of said other electrolyte salts relative toall the electrolyte salts is 0.01 to 45%.
 15. A lithium secondarybattery comprising a positive electrode, a negative electrode, and anonaqueous electrolytic solution which includes an electrolyte saltdissolved in a nonaqueous solvent, wherein the nonaqueous electrolyticsolution comprising the nonaqueous electrolytic solution according toclaim
 7. 16. The lithium secondary battery according to claim 15,wherein the positive electrode is made of a material containing alithium compound metal oxide and the negative electrode is made of amaterial containing graphite.